1. Field of the Invention
The present invention relates to an electric vehicle, such as an in-wheel motor vehicle, that is equipped with motor(s) to drive wheels and that may be battery-powered or fuel cell-powered. The present invention also relates to an in-wheel motor drive system that may be associated with a drive wheel of a vehicle that may be an electric vehicle. The present invention also relates to a method of controlling a motor unit.
2. Description of Related Art
An electric vehicle may experience degradation in performance or malfunctions of a motor serving as a drive for the vehicle. This can significantly affect the travel performance or travel safety. Reliability of a motor, a wheel bearing and a reducer is an urgent concern for an in-wheel motor drive system which, due to its smaller size, has less materials used, involves rapid rotation of the motor, and etc.
A battery-powered electric vehicle may include a drive system which may be in the form of an in-wheel motor drive system. The drive system may employ an IPM (e.g., Interior Permanent Magnet synchronous motor). Such an IPM may include a neodymium magnet to provide a highly efficient performance, thus increasing the maximum travel range that is possible with a limited battery capacity.
In the past, in the attempt to ensure such reliability, an in-wheel motor drive system has been proposed in which the temperature of components such as a wheel bearing, a reducer and a motor may be measured and monitored for overload, with features to limit a drive current in/to the motor or a rotational frequency of the motor according to the temperature measurements (see the Patent Document 1 listed below).    [Patent Document 1] JP Laid-open Patent Publication No. 2008-168790